Charge stabilizer for heat pump



Nov. 27, 1962 w. E. MAUDLlN CHARGE STABILIZER FOR HEAT PUMP Filed Aug. 9, 1960 INVENTOR WENDELL E. MAUDLIN ATTORNEY United States Pa ent() 3,065,610 CHARGE STABILIZER FOR HEAT PUMP Wendell E. Maudlin, Lebanon, lnd., assiguor to Stewart- Warner Corporation, Chicago, Ill., a corporation of Virginia Filed Aug. 9, 1960, Ser. No. 48,401 2 Claims. (Cl. 62-149) absorbs heat from the surroundings during the heat pump cooling cycle, or dissipates heat to the surroundings during the heat pump heating cycle.

Refrigerants commonly used in such a cycle are ammonia and a variety of Freons under the trade names of Freon ll, Freon l2, Freon 22, Freon 113 and Freon 114, as Well as the common gases of carbon dioxide, sulphur dioxide, methyl chloride, and water vapor.

For cooling an enclosure the vaporous refrigerant is compressed and directed to a coil located outside of the enclosure or an outdoor coil. The ambient temperature of the outdoor coil is belowthe condensing temperature of the compressed vapor. The vapor condenses to a liquid at approximately the same pressure. The compressed liquid is then directed to a coil located within the enclosure, or an indoor coil. The pressure of the compressed liquid is throttled and the liquid vaporizes or boils in the indoor coil absorbing heat from the surroundings approximately equal to the heat of vaporization of the refrigerant. The vapor from the indoor coil is then recompressed to repeat the cycle.

For the heating cyclethe compressed vapor is directed to the indoor coil. This coil condenses the vaporous refrigerant to a compressed liquid. The condensation dissipates heat to the surroundings approximately equal to the heat of vaporization of the refrigerant. An expansion valve regulates the flow of liquid refrigerant to the outdoor coil where the heat of the outdoor air boils the refrigerant. The vapor is then recompressed to repeat the cycle. I

Heating and cooling cycles of a closed heat pump circuit are controlled by a 4-way reversing valve operable to direct the compressed refrigerant gas to either theindoor coil or the outdoor coil. The outdoor coil acts as the condenser and the indoor coil acts as the evaporator during the cooling cycle, while the indoor coil acts as the condenser and the outdoor coil acts as the evaporator during the heating cycle.

For highest operating efliciency both the condensing and vaporizing sequences of the cycle should be totally completed before the refrigerant leaves the respective coils. In other words, the conveying lines leading to and from the condenser coil should contain all compressed vapor and compressed liquid, respectively, while the conveying lin'es leading to and from the evaporator coil should contain all compressed liquid and expanded low pressure vapor, respectively.

It has been found that a greater quantity of refrigerant is required for the heating cycle than for the cooling cycle. The quantity of refrigerant used in a prior art heat pump circuit has been a compromise based on the average conditions expected of the heat pump. Consequently, during the heating cycle the quantity of refrigerant has been insufficient. Vaporous refrigerant is then circulated without the process of complete condensation. This reduces the effectiveness of the heat transfer surface and requires compressor power input with little or no resultant heating effect derived from the uncondensed portion of refrigerant. Conversely, during the cooling cycle the quantity of refrigerant is excessive. The refrigerant then backs up through the condenser coil into the lines which reduces the available condensing surface thereby raising condensing temperatures causing increased compressor power input and reduced capacity. This comprising with the quantity of refrigerant in the circuit reduces the efiiciency of the heat pump for both the heating and cooling cycles, since all of the refrigerant is not performing useful work. I

Accordingly, a principal object of this invention is to provide means for adjusting the quantity of refrigerant in a heat pump circuit during the heating and cooling cycles to give optimum efficiency for both cycles.

A feature of this invention is a charge stabilizer communicating' with the heat pump circuit. The=circuit in cludes a circulating charge of refrigerant of such quantity to give optimum efliciency during the heating cycle. The charge stabilizer withdraws a portion of that charge during the cooling cycle for providing the lesser quantity of circulating refrigerant that ensures optimum eflii and 12 to a 4-way reversing valve 13 and an accumulator 14. Line 16 connects the reversing valve to one end of outdoor coil 18. The coil 18 is located outside of the enclosure to be conditioned in heat-exchange relationship with the outdoor air. Line 20 connects the other end of coil 18 to a parallel juncture having check valve 22 comprising one leg, and expansion valve 24 and filter drier 26 comprising the other leg. A valve control 27 extends between the expansion valve to the outdoor coil.

Line 32 including liquid indicator 28 and service valve 30 communicates the rejoined parallel juncture with another parallel juncture. The second parallel juncture has check valve 34 and lines 35 comprising one leg, and a distributor and strainer 36 and capillary tubes 37 com prising the other leg. Lines 35 and 37 join and communicate with corresponding ends of indoor coils 38. Coils 38 are located within-the enclosure to be condi tioned in heat exchange relationship with theindoor air. Lines 40 from corresponding ends of coils 38 unite and communicate through line 42 andservice valve 44 with the reversing valve 13. The circuit is thus completely enclosed at all times. Service valves 30 and 44 are'for servicemen to gain access to the circuit for evacuating, adding refrigerant or reading pressures. The valves also serve as shut-off valves so that the outdoor section can be shipped sealed. Liquid indicator 28 gives visual indication of the liquid refrigerant at the outlet of the condenser coil. If bubbles are present, insuflicient refrigerant charge is generally indicated.

This invention provides a charge stabilizer 46 which is preferably located on line 20. Line 20 is the inlet of coil 18 for the heating cycle and the outlet of coil 18 for the cooling cycle. The charge stabilizer 46 is a hollow fluid-tight tank constructed of material with sufficient strength to withstand the high side operating pressures of the heat pump cycle. The charge stabilizer is in an inverted position and has a port 48 communicating with line 20. Port 48 preferably is lower than the remainder of the tank so that any liquid collected in the tank can be quickly dumped by gravity to line 20. The charge stabilizer is in heat exchange relationship with the outdoor air.

With the heat pump circuit as shown in the FIGURE, the quantity of refrigerant required during the heating and cooling cycles is automatically adjusted to give the optimum performance for both cycles. A specific quantity or charge of refrigerant can be included in the circuit for the heating cycle to give optimum efliciency for the designed conditions. Similarly, the cooling cycle employing the same circuit would require a different specific quantity or charge of refrigerant to give optimum efficiency for given design conditions. The difference in the quantity of refrigerant required to give optimum efficiency during the heating and cooling cycles can then be determined. This difference represents the quantity of refrigerant which the charge stabilizer must accommodate. The volume of the charge stabilizer to accommodate this difference thus is determined.

During the cooling cycle, vaporous refrigerant is compressed and directed through 4-way valve 13 and line 16 to the outdoor coil. The compressed vaporous refrigerant then condenses to a compressed liquid and flows through line 20, check valve 22, and line 32 to distributor and strainer 36'. The capillary tubes then throttle the high pressure liquid causing the liquid to vaporize. The refrigerant vaporizes within the indoor coils 38 cooling the coils and absorbing heat from the indoor air flowing over the coils. The vapor then flows through lines 40 and 42 to 4-way valve 13 and by line 12 to the accumulator 14. Accumulator 14 separates any remain- I ing liquid droplets from the vapor mixture before the vapor is recompressed to repeat the cycle, thus preventing damage to the compressor.

During the heating cycles the compressed vapor is directed by the reversing valve 13 through lines 42 and 40 to the indoor coil. Indoor coil condenses the compressed vapor to a compressed liquid. The condensa tion dissipates heat through the coil to heat the indoor air flowing over the coils. The compressed liquid is then directed through check valve 34, line 32 to the filter drier 26. The filter drier removes dirt or foreign matter and dries the refrigerant of water by chemical action. Expansion valve 24 then throttles the liquid refrigerant to the outdoor coil where it is boiled by the heat of the outdoor air to vaporous refrigerant. Valve control 27 regulates the expansion valve by temperature or pressure sensing means as is well known in the art. The vapor is returned by line 16 to 4-way valve 13 and by line 12 through the accumulator to the compressor 10 for recompression.

' Thus the heating and cooling cycles utilize the same circuit varying only the direction of refrigerant flow which is regulated by 4-way reversing valve 13.

During the heating cycle all of the refrigerant will be used effectively within the circuit. The refrigerant will be a low pressure vapor in the outdoor coil and the charge stabilizer. When reversing valve 13 is actuated to the cooling cycle, the refrigerant entering the outdoor coil is a high-pressure vapor. The outdoor coil condenses the refrigerant, and the charge stabilizer withdraws the excess liquid refrigerant from the active heat pump circuit. The pressure of the refrigeration line 20 is sufficient to maintain the liquid refrigerant in the charge stabilizer against the vapor pressure of the refrigerant. During the cooling cycle the charge stabilizer would be filled with condensed refrigerant.

The charge stabilizer also regulates the quantity of refrigerant used during an automatic defrosting cycle. During the heating cycle, frost can accumulate on the outdoor coil if the temperature of the outdoor air is below freezing. The accumulated frost can be defrosted by interrupting the heating cycle and temporarily reversing the flow of the refrigerant with reversing valve 13. The compressed vapor is thus directed by line 16 to outdoor coil 18. Since the temperature of the air surrounding the outdoor coil and the charge stabilizer is substantially below the vaporization temperature of the compressed refrigerant, the refrigerant readily condenses within the coil and charge stabilizer. The heat given off by the refrigerant condensing melts the frost on the outdoor coil. The excess refrigerant during the defrost cycle is effectively withdrawn from the active circuit and stored in the charge stabilizer until the defrost cycle is completed and valve 13 is reversed to resume the heating cycle. The pressure of the refrigerant in the charge stabilizer then drops below the vaporization pressure and the refrigerant boils to a vapor. Thus the proper quantity of refrigerant is insured for all operations of a heat pump to give optimum efficiency.

What is claimed is:

1. In a heat pump operable to air-condition an enclosure, the heat pump having a refrigerant circulating in a closed circuit including a compressor, an indoor coil located within the enclosure, an outdoor coil located outside of the enclosure, a reversing valve for selectively controlling the flow direction of the refrigerant for the heating and cooling cycle, and pressure throttling means between the indoor and outdoor coils operable to reduce the pressure of the refrigerant flowing therethrough to below the vapor pressure of the refrigerant corresponding to the ambient temperature of the respective coil acting as the evaporator coil, the improvement comprising a charge stabilizerconsisting of a fluid-tight tank located outside of the enclosure and having a refrigerant communicating connection substantially at its lowest point with the circuit between the throttling means and the outdoor coil, said charge stabilizer being operable to withdraw automatically a portion of the refrigerant from the active circuit during the cooling cycle by the varying vapor pressures of the refrigerant during the heating and cooling cycles, respectively.

2. A heat pump for an enclosure, comprising an indoor coil within the enclosure, an outdoor coil outside of the enclosure, pressure throttling means interconnecting one end of each coil, a compressor, a 4-way valve interconnecting theother end of each coil and the compressor and completing a closed heat pump circuit, said 4-way valve being operable to connect the output of the compressor directly to the indoor and outdoor coils respectively during the heating and cooling cycles of the heat pump, a given charge of refrigerant in the heat pump circuit to render optimum performance for the heating cycle, and a charge stabilizer of volume comparable to the refrigerant in the liquid state excessive from the given charge to render optimum performance for the cooling cycle, Said charge stabilizer being disposed outside of the enclosure and having a communicating connection with the heat pump circuit between the 4-way valve and the pressure throttling means in the portion of the circuit including the outdoor coil.

References Cited in the file of this patent UNITED STATES PATENTS 

